archer_project_board_power_supply_277-125_manual

POWER SUPPLY

CATALOG NUMBER 277-125

This PROJECT BOARD POWER SUPPLY provides 5 volt or 1 3.8 volt power. It also, at the option of
the buyer, may bebuiltupasa5v/13.8vdual power supply. As a 5 volt power source it may be
used in any 7400 or 74LS00 series digital logic such as computers, ASC II and other digital
circuits. The 13.8 volt option may be used as a power source for a CB radio, automobile
radio/tape player or any other automotive accessory needs.

Photograph is the completed project when built with the recommended Radio Shack parts. This
package contains only the Printed Circuit Board, and Assembly/Operating Instructions.

CUSTOM MANUFACTURED IN U.S.A. BY RADIO SHACkSa DIVISION OF TANDY CORPORATION

POWER SUPPLY

Table of Contents

Introduction .2

Specifications.2

Theory Of Operation .2

Parts List.3

Mounting Parts On PC Board.4

Preparing Cabinet.9

Mounting Components In Cabinet.9

Preparing and Mounting Transformer.11

Cabinet Wiring.12

Installing and Wiring Project Board.12

Final Checkout & Adjustment.13

Front Panel Layout Template.13

Back Panel Layout Template.16

Cabinet Bottom Layout Template.16

Schematic.17

INTRODUCTION

This Project Board is designed to be used wherever and whenever you need a regulated source of 5 volts or 13.8
volts DC at 1 Ampere. You can build the Project Board to provide either 5 or 13.8 volts (or both, with just a couple
of changes in wire jumpers). We've written the instructions to tell you how to use either option (by adding or
omitting parts and jumper wires). Check the Parts List before you obtain parts—that way you won't end up with
unneeded parts.

CAUTION: A selector switch could have been used in place of the jumper wires for voltage selection.
However, the danger of inadvertently selecting the wrong supply could damage expensive equipment:
therefore A SWITCH IS NOT RECOMMENDED.

SPECIFICATIONS

GENERAL

Input .103 to 135 VAC

Output .5.0 or 13.8 VAC (+10%) (Internally Adjustable)

Operating Temperature .0° to 50°C

Cooling .Convection

ELECTRICAL
Output Voltage Effects

1. Due to AC input source

variation (105-135 VAC).

2. Due to load variations (0-1 Amp)

Ripple.

Short Circuit Current.

THEORY OF OPERATION

The heart of the power supply is the LM317 adjustable voltage regulator 1C. This regulator has built-in protection
from short circuits, excess current and excess temperature. The adjustable voltage feature is determined by an
external resistor network.

For 5 volt operation, the transformer and two diodes (CR2 and CR3) form a full-wave center-tapped rectifier
circuit which suppliesabout 10 volts DC. Forthe 13.8 volt operation, four diodes (CR1 thru CR4)are used toform a
full-wave rectifier circuit which supplies about 20 volts DC.

Capacitors Cl and C2 provide filtering for the rectified DC and remove most of the ripple.

The output voltage is determined by a resistor divider network of either R2, R3 and R5 (for 5 volt operation) or R2,
R4 and R6 (for 13.8 volt operation). The voltage divider is set up so that the voltage drop between the "output" and
"adjust" pins of the LM317 is 1.25 volts. Adjustable resistors (R3 for 5 Volts and R4 for 13.8 Volts) allow exact
setting of the output voltage.

100 mV
200 mV

20 mVRMS maximum (5 mVRMS typical)
Self-limiting

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POWER SUPPLY

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Capacitor C3 is used to reduce the ripple on the "adjust" pin of the Ll\/1317 which further reduces the ripple
present at the "output" of the regulator. Capacitor C4 improves the transient response of the voltage regulator.

The power supply will maintain 5 volts or 1 3.8 volts at 1 Amp under power line variations from 1 05 VAC to 1 35
VAC. It will be a quality addition to your electronic workshop when built with proper,care.

CAUTION: Although the LM317 can be adjusted to any value from 1.25 volts to 37 volts, operation of
the power supply at voltages or currents other than those specified can cause overheating of the
regulator, poor regulation or other malfunctions.

PARTS LIST

PARTS QUANTITY

PFR nPTiriM

RADIO SHACK
CATALOG #

SYMBOL

DESCRIPTION

5 VOLT

13.8 VOLT

Cabinet

270-268

1

1

Spacers, 1/4 In.

64-3024

1 Pkg,

1 Pkg.

Screws, #6-32 x 1/2 In. Lg.

64-3012

6

6

Nuts, #6-32

64-3019

1 Pkg

1 Pkg

Line Cord

278-1255

1

1

Strain Relief

278-1636

1 Pkg

1 Pkg

SW1

Switch SPOT

275-612

1

1

FI

Fuse* Holder

270-364

1

1

Fuse, 3/4 Amp

270-1272

1 Pkg

1 Pkg

Binding Posts, 1 Red, 1 Black

274-662

1 Pkg

1 Pkg

T1

Transformer 1 8 VCT @ 2.0 Amp

273-1515

1

1

Printed Circuit Board

277-125

1

1

R1

56 Ohm 1 Watt Resistor

271-072

—

1 Pkg

R2

270 Ohm 1/4 Watt Resistor

271-1314

1 Pkg

1 Pkg

R3

500 Ohm Trim Pot (Adj Resistor)

271-226

1

—

R4

1 K Trim Pot (Adj Resistor)

271-227

—

1

R5

470 Ohm 1 /2 Watt Resistor

271-0019

1 Pkg

—

R6

2.2K 1/2 Watt Resistor

271-0027

—

1 Pkg

Cl & C2

1000/Lt F 35VDC Electrolytic Capacitor

272-1032

2

2

C3 & C4

3.3# F 35VDC Tantalum Capacitor

272-1408

2

2

CR1 thru
CR4

1 Amp IN-4001 Diodes

276-1101

1 Pkg

2 Pkgs

IC1

LM317 Voltage Regulator

276-1777

1

1

TO-3 Mtg Hdw (Insulators,

Washers, Nuts, Screws)

276-1371

1

1

TO-3 Heatsink

276-1364

1

1

3 Color Pack, 18 Gauge Stranded Wire

278-1303

1

1

Heatsink compound

276-1372

1

1

3 Color Pack, Solid Wire^

278-1295

1 Pkg

1 Pkg

Solid #24 Bus Wire* "

278-1341

Optional

Optional

"Used for jumpers instead of solid wire.

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POWER SUPPLY

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BEFORE YOU BEGIN;

□ Check your parts against the Parts List. Be sure the parts are correct.

□ Make sure your soldering iron is no more than 40 Watts and has a fine point for delicate work. Clean the tip
often. Use high quality solder such as Radio Shack 64-006.

□ A good solder connection Is shiny and is only slightly larger than the connection point. Constantly watch for
splatters which might bridge adjacent connections unintentionally.

□ When installing a component on the PC Board, insert the leads through the illustrated side of the board; bend
the leads slightly to hold the part in place. Solder and clip the lead from the foil side.

□ When you connect wires or leads to terminals, you must make a good mechanical connection before
soldering. Wrap the lead tightly around the terminal and clamp it firmly with your pliers.

□ Familiarize yourself with the schematic, board, parts and instructions before you begin.

□ One last word . . . the Project Board is supposed to be fun, so TAKE YOUR TIME, relax and enjoy yourself.

NOTE: A word of warning right at the beginning—if you run into problems when you're done (we hope
you won't. . .but if you do. . .) 9 times out of 10 it will be because of poor soldering. Also watch for
proper parts identification and installation.

MOUNTING THE PARTS

We've carefully considered the sequence of construction — to make it as easy as possible. So we
recommend you follow our manual carefully. You have three options in assembling your power supply.
You can build it for 5 volt or 13.8 volt operation, or if you choose, with both 5 volt and 13.8 volt
capability.

The parts for the 5 volt operation are shaded like this in the illustrations.

The parts for the 13f8 volt operation are striped like this.

The parts used when assembling for both 5 volt and 13.8 volt will appear both shaded and striped.

To aid you with your construction, a "check box" has been provided at the left of each part listing. Check off
each "box" 0 as you mount the part.

NOTE: Be careful to include all steps. The check box will keep you from omitting a step, a mistake that
is more common than you might think!

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POWER SUPPLY

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MOUNTING RESISTORS (See illustration 1)
Mount the following resistors:

5 volt operation

□ R2, 270 Ohm (Red, Violet, Brown)

□ R5, 470 Ohm (Yellow, Violet, Brown)

□ R3, 500 Ohm adjustable Potentiometer

13.8 volt operation

□ R1,0.56 Ohm, rectangular shape

□ R2, 270 Ohm (Red, Violet, Brown)

□ R6, 2.2K Ohm (Red, Red, Red)

□ R4, 1K Ohm adjustable Potentiometer

□ Turn the board over and solder. Trim off any
excess lead lengths.

Illustration 1. RESISTOR INSTALLATION DIAGRAM

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MOUNTING DIODES (See Illustration 2)

The next step is to mount the diodes. These parts
must be installed with the banded end (cathode)
positioned as illustrated. The cathode end may be
identified by any of the markings commonly used on
diodes as shown in the example.

ANODE )
END \

CATHODE

^ END

Mount the following diodes: (See Illustration 3)

Illustration 2. DIODES

5 volt operation

□ CR2 and CR3 Diodes

1 3.8 volt operation

□ CR1, CR2, CR3 and CR4 Diodes

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Illustration 3. DIODE & CAPACITOR INSTALLATION DIAGRAM

POWER SUPPLY

MOUNTING CAPACITORS (See Illustration 3)

The next four parts are capacitors and they must be
installed with the leads going into the correct holes.
The leads will have + and/or - markings; be sure to
correctly identify the lead markings before installing
these parts.

All four capacitors are needed for both versions.

□ Cl, lOOOfi F electrolytic capacitor. Be sure to
install with the + and/or - leads correctly.

□ C2, ^000fl F electrolytic capacitor. Be sure to
install with the + and/or - leads correctly.

C3 and C4 are tantalum-type capacitors. The polarity
markings may be a little less obvious. Note the detail
drawings supplied to aid you in correctly identifying +
and - leads.

□ C3, 3.3fi F tantalum capacitor. Be sure you
install with the + lead into the correct hole.

□ C4, 3.3/i F tantalum capacitor. Again, be sure to
install the + lead in the correct hole.

MARK

PLUS LEAD
CLOSEST TO
MARK-

+

Units marked with + are easy. The lead
closest to the + mark is the + lead.

Units with a color dot may cause some
confusion. Hold the Tantalum capacitor
so the color dot faces you: the lead on
your right is the + side.

□ Turn the board over and solder. Trim off excess
lead lengths.

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POWER SUPPLY

MOUNTING VOLTAGE REGULATOR

(See Illustration 4)

□ To insure that the Heat Sink will not interfere
with the rest of the unit, you'll have to bend in the
flanges of one side. Refer to Figure lOtoseehow
the part will be installed. Now carefully bend in
the flanges of the Heat Sink that will be next to
the Binding Posts. Bend about 3/8" (10 mm).

□ Now apply Radio Shack Cat. No. 276-1372 Heat
Sink Compound on the surface of the Heat Sink
which will be in contact with the LM 31 7 Voltage
Regulator.

□ Position Heat Sink and Voltage Regulator as
shown in Illustration 10 with the flanges of the
Heat Sink up away from the Board and the pins of
the 1C down through the Board. (Bent flanges
next to the edge of the Board.)

□ Insert the 1C pins through the Board making sure
they protrude through the PC Board.

□ Fasten the 1C and Heat Sink to the PC Board with
two 6-32 X 1 /2" screws and nuts. Insert so the
screw-heads are on the foil side of the Board.
Tighten nuts.

n Solder 1C pins and cut off excess lead lengths.

INSTALLING JUMPER WIRES

Points ABC and DEF on the Board determine the
output voltage; either 5 or 13.8 volts. Remove the
insulation from a length of solid hookup wire (RS Cat.
No. 278-1295) and use the stripped wire for your
jumpers or use 24-gauge bus wire (RS Cat. No. 278-
1 341). Use jumper wires cut to a length equal to the
point-to-point wire location on the Project Board, plus
enough to protrude through the Board for soldering.
After you have soldered the jumpers cut off any
excess length.

n For 5-volt operation, install jumper wires
between B and C, and E and F.

□ For 13.8-volt operation, install jumper wires
between A and B, and D and E.

Illustration 4. 5 VOLT JUMPER WIRE AND VOLTAGE REGULATOR INSTALLATION

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POWER SUPPLY

CHECK YOUR WORK. . .now that the Board is completed.

□ Check all solder connections to be sure they are clean, shiny and secure.

n Make sure none of the foil has pulled up from the board due to excessive heat.

□ Be sure that no solder has flowed across/between foil paths.

PREPARING CABINET

□ Front Panel: Using the Front Panel Layout Template drawing supplied at the back of this Manual, mark and
punch locations for On-Off switch (SW1) and binding posts. Drill 1 /4" (6.4mm) switch mounting hole. Use a
5/16" (8mm) drill for the Binding Posts.

Rear Panel: Using the Rear Panel Layout Template, markand punch locationsforthe Fuse Holder and power
cord strain relief. Drill 5/8" (12.7mm) mounting holes.

□ Cabinet Bottom: Using the Cabinet Bottom Layout Template markand punch locationsforthe PC Board and
the Transformer mounting screws. Drill four 11/64" (4mm) holes for mounting the PC Board and two
11 /64" (4mm) holes for mounting the Transformer.

□ Front Panel Label: Remove the paper backing and carefully align the label over the Front Panel and press
into place.

MOUNTING COMPONENTS IN CABINET

□ Switch SW1: Mount Switch in the hole drilled inthe Front Panel andtighten nut. See Illustration 6. Position
with slot so that Switch is ON when handle is in up position.

□ Binding Posts: Mount in front panel with the black post on your right and the red post on your left (as viewed
from the front) and tighten nuts. See Illustration 6.

Q Fuse Holder FI : Mount Fuse Holder in back panel and tighten nut. See Illustration 7 for positioning.

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POWER SUPPLY

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Installing Strain Relief Bushing

1. Position the Strain Relief Bushing at the wire
separation point.

2. Squeeze the segments together.

3. Insert line cord and strain relief into panel.
Press firmly to seat the strain relief.

Illustration 9 STRAIN RELIEF INSTALLATION

PREPARING AND MOUNTING
TRANSFORMER

□ Cut two 1 8-gauge black stranded lead wires. The
first black wire should be 10" (25cm). The other
black wire should be 6" (15cm). Remove 1/4"
(6.4mm) of insulation from each end of both
wires and apply a light coat of solder to the bare
wire ends.

□ Connect one black wire to one terminal of the
Primary (PRI) side of the Transformer and the
other black wire to the second connection. Solder
both connections.

□ Cut three 18-gauge stranded lead wires: 2 red
and 1 green 3" (7.5cm) long. Remove 1/4"

(6.4mm) of insulation from each end of both
wires and apply a light coat of solder to the bare
wire ends.

□ Connect the Green wire to the center terminal of
the Secondary (SEC) side of the Transformer.
Connect the two red wires to the remaining
terminals of the Secondary (SEC) side. Solder all
three connections.

□ Install the Transformer in the cabinet using two
#6-32 screws and nuts, with the screw heads on
the bottom of the Cabinet. Position the Primary
(PRI) side toward the rear of the Cabinet.

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POWER SUPPLY

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CABINET WIRING

□ Solder the short line cord leadtoterminal 1 of the
Fuse Holder (See Illustration 7).

L Solder the long line cord lead to terminal 2 of
SW1 (See Illustration 6).

□ Connect one black primary lead from the
Transformertoterminal 2of the Fuse Holder (See
Illustration 7).

□ Connect the other black primary lead from the
Transformer to terminal 1 of SWl (See Illustra¬
tion 6).

WARNING: We strongly recommend that
you use electrical tape and cover alt of the
exposed AC connections. A SHOCK
HAZARD EXISTS AT THESE POINTS. They
are:

1. SWl On-Off Switch, two connections

2. FI Fuse Holder, two connections

3. T1 Transformer, Primary side, two connec¬
tions

□ Position the PC Board in the Cabinet as shown in
Illustration 10 but do not fasten with screws.

□ Solder the Transformer secondary green center
lead to CT on the PC Board (See Illustration 10).

C Solder one of the red transformer secondary
leads to the nearest AC connection point on the
PC Board. Solder the remaining transformer
secondary lead to the remaining AC connection
(See Illustration 10).

□ Cut two 6" (1 5cm) 18-gauge stranded lead wires,
1 red and 1 black. Remove 1/4” (6.4mm) of
insulation from each end of both wires and apply
a light coat of solder to the bare wire ends.

□ Connect black wire to the negative (-) terminal on
the PC Board and the red wire to the positive (+)
terminal on the PC Board and solder both
connections.

□ Connect and solder the black wire to the Black
Binding Post and the red wire to the Red Binding
Post.

□ Fasten the PC Board in position with four 6-32
screws, spacers, nuts and washers. (Install
1 /4" spacers between the Cabinet and PC
Board.) Be sure no lead wires or solder connec¬
tions extend below the spacers to touch the metal
cabinet.

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Illustration 10. CHASSIS WIRING ILLUSTRATION

POWER SUPPLY

FINAL CHECKOUT AND ADJUSTMENT

□ Check all solder connections and make sure all
are making positive contact.

□ Make sure there are no damaged components,
such as cracked resistors, a broken or frayed
wire, fuse holder or binding post, etc.

□ Make sure all mechanical connections and
screws and nuts are tight.

□ Install 3/4 Amp fuse in Fuse Holder.

□ Adjust R3 and R4 to the center of their range.

□ Plug power cord into a source of 1 20VAC power.

□ Connect a voltmeter to the binding posts and note
the output voltage. If the voltage reading is not
exact, use a screwdriver and adjust the trim pot
(adjustable voltage regulator) as shown in
Illustration 11 until the voltage desired is ob¬
tained.

Illustration 11. ADJUSTING THE TRIM POT

WARNING: Before you install the cover,
be sure ail wires and parts are positioned
away from the holes where the screws
come through Do not allow the points of
the screws to pierce through the wire's
insulation or touch circuit connections.

□ Install Cabinet cover and fasten with screws and
washers provided. Position the vented section of
the cover over the PC Board.

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(12.0mm)

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RADIO SHACK ^ A DIVISION OF TANDY CORPORATION

U.S.A.: FORT WORTH, TEXAS 76102
CANADA; BARRIE, ONTARIO L4M 4W5

TANDY CORPORATION

AUSTRALIA BELGIUM U K

280-316 VICTORIA ROAD PARC INDUSTRIEL DE NANINNE BILSTON ROAD WEDNESBURY
RYDALMERE. N S W 2116 6140 NANINNE WEST MIDLANDS WSIO 7JN

878-TM-100-1126

PRINTED IN USA